DESCRIPTION: Black men who have sex with men (MSM), especially young MSM, are disproportionately affected by HIV, with an annual incidence higher than any other age or race group. Despite this increasing epidemic, few studies have focused on MSM nor accounted for these disparities. The research that has examined disparities in MSM has been focused on understanding individual-level behavior, but this has been inadequate to explain HIV racial disparities. Additionally, network research is increasingly a priority area in HIV research due to the disease's high transmission dependence on drug and sexual network dynamics. However, network descriptions alone are also inadequate without considering the interplay of individual and contextual factors. Instead, it has been suggested that a broader systems-level perspective may be necessary as several interacting individual, network, and contextual differences may account for the increased epidemic in Black MSM populations. Due to this call for a systems-level perspective in understanding and preventing HIV infection, this grant seeks to advance understandings of HIV racial disparities in MSM by examining individual, sexual network, and social contextual factors within a multilevel network model. This model will be tested within an exceptional U01 NIDA-funded cohort of 1,200 diverse Chicago YMSM (PI: Primary Mentor Mustanski), which is collecting original multilevel (biologic, individual, dyadic, network) data. Utilizing methods developed within the applicant's R03 Project, YMSM will complete social (social, sexual, drug) and contextual (neighborhood & venue) network interviews. Building the study into the U01 cohort allows the current project to benefit from the strong infrastructure and resources of the U01, fortifies this project's feasibility, and provides unique opportunities to expand the aims of the U01. Data from this comprehensive longitudinal multilevel dataset will be used to build and validate a model of social contextual influences on racial disparities in HIV through innovative analyses and methods that account for the complex dynamics of HIV transmission and racial disparities. The overall project has two aims: 1) Identify social contextua factors (i.e., social relational and social contextual) which contribute to racial disparities in HV and 2) Examine the interplay of individual, sexual network, and social contextual factors in racial disparities in HIV. Additional sub- aims include: A) Compare the contribution of each level of analysis to racial disparities in HIV using innovative Multiple-Membership Multiple-Classification Models (MMMC) and B) Understand and validate the relations of individual, sexual network, and social contextual structures and attributes to racial disparities in HIV with ERGM.